This application claims the priority of German patent document 103 28 279.3, filed Jun. 23, 2003 (PCT International Application No. PCT/DE2004/001260, filed Jun. 17, 2004), the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for the evaluation of the received signals in a SAR/MTI pulsed radar system.
Synthetic Aperture Radar/Moving Target Indication (SAR/MTI) pulsed radar systems, can be used both to acquire SAR images and to identify moving targets in the acquired images. FIG. 1 shows the pulse sequence of a transmitted signal of a SAR/MTI pulsed radar system. Because of the different illumination times that are required to achieve a high resolution with the respective evaluation methods, the pulse repetition frequencies of the transmitted SAR and MTI pulses differ considerably. For a typical SAR evaluation, an illumination time T SAR of more than ten seconds is possible. However, the illumination time T MTI of a ground area for identifying and tracking moving targets normally amounts to 100 ms.
FIG. 2 shows a received echo pulse sequence which essentially is a superimposition of SAR and MTI echo pulses. In known SAR/MTI radar systems, the signal evaluation takes place such that the acquisition and generation of SAR images and the analysis of the SAR images by means of MTI processes for identifying moving targets, take place in time sequence. Normally, a SAR image is acquired first, and is subsequently examined in an MTI process with respect to moving targets.
Simultaneous analysis of the signals in a SAR and an MTI process can therefore be carried out only at great technical expense. For known processes for evaluating signals in SAR/MTI radar systems, the received signal is divided into two approximately identical components, and one part of the signal is fed to a device for SAR signal evaluation, while the other is fed to a device for MTI signal evaluation. In this case, however, it is disadvantageous that the radar system, particularly the radar antenna, comprises a large number of constructional elements, and requires high technical expenditures. This results in additional disadvantages with respect to the considerable weight of the antenna. Another disadvantage is the large dimension of the antenna, which makes it difficult to integrate it in a flying device.
It is therefore an object of the invention to provide a process which allows simultaneous evaluation of the received signals with respect to the SAR and the MTI, without high technical expenditures.
Another object of the invention is to provide an antenna for implementing the process.
These and other objects and advantages are achieved by the method and apparatus according to the invention, in which, in the received echo pulse sequence of the received signal, each pulse that corresponds to an integral multiple of an integral ratio of the pulse repetition frequency PRF MTI of the transmitted MTI signal to the pulse repetition frequency PRF SAR of the transmitted SAR signal, and which is received after a transmitted SAR pulse, is evaluated in a SAR process. According to the invention, the remaining pulses of the received echo pulse sequence are evaluated in an MTI process, and the pulse for the MTI signal processing which is absent as a result of the SAR signal processing, is reproduced by means of an interpolation method.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.